Thermionic amplifier.



A. McL. NICOLSON.

THERMIONIC AMPLIFIER.

APPLICATION FILED MAY 19, m5.

Patented Jan. 2,1917. F/g 2 SHEETSSHEETI mvenfor A/Iy [alaialela flma II l I I I as? W M Alexander NH em A/fco/son.

A. McL. NICOLSON.

THERMIONIC AMPLIFIER.

APPLICATION FILED MAYIQ, I915.

Patented Jan. 2, 1917.

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ALEXANDER MOLEAN NICOLSON, OF NEW YORK, N. Y., ASSIGNOR, BY MESNEASSIGN- MENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATIONOF NEW YORK.

Specification of Letters Patent.

Patented an. 2, 1917.

Application filed may 19,1915. Serial No. 29,077.

-fiers, and more particularly to an improved organization of electrodesfor the purpose of producing a large output therefrom.

In a copending application, Serial No. 21,918, I have described theadvantages to be derived from the use of a so-called equipotentialcathode in a thermionic amplifier, that is, a cathode surface, all partsof which are at the same potential with respect to the anode. v

This invention provides for rendering such a cathode surface active byelectronic bombardment from another cathode.

It further provides for the employment of a series of such cathodesurfaces of successively increasing electron-emitting capacity, in anarrangement for increasing the volume of the cathode stream, eachcathode surface being rendered active by bombardment from the precedingcathode of the series.

The invention further provides for the association of such a series ofcathodes with one or more input electrodes whereby the magnitude of sucha cathode stream may be varied at any stage of its amplification inaccordance with variations in a relatively feeble input energy which itis desired to amplify.

For a more complete understanding of the invention, reference may be hadto the accompanying drawings in which- Figure 1 represents a simplethermionic repeater arrangement employing an equ1-. potential cathoderendered active by thermionic bombardment, Fig. v2 glves a fragmentaryview of a modification of the arrangement of Fig. 1; Fig. 3 representsan arrangement for the amplification of energies in which a plurality ofinputelectrodes are employed for the purpose of increasing thevariations in magnitude of the thermionic stream; and Fig. 4 shows infragmentary detail a mechanical arrangenperi t of the electrodes used inthe system 0 .3.

Re erring to Fig. 1, 10 is the customary highly evacuated vesselinclosing an anode 11, a grid or input electrode 12, equipotentialcathode 13 and auxiliary cathode .or filament 1 1. The cathode 14 may beof tungsten or of platinum suitably coated with a thermionically activematerial, such as a mixture of strontium and barium oXids, and whenheated to incandescence by battery 15 emits a stream of electrons whichwill bombard the cathode 13 by virtue of the fact that cathode 13 ismaintained positive with respect to filament 14 by means of battery 16.Cathode 13 is preferably made from thin sheet metal, such as platinum ortungsten, and has a thermionically active coating applied to the sideaway from the filament 14, which produces the bombarding electronicstream. The cathode 13 is heated by this bombardment and becomeselectronically active, and by virtue of the larger active surface andenergy imparted to the system by battery 16, the volume of itselectronic emissions will be much greater than that of the filament 14.It is thus seen that the arrangement of two cathodes here employedprovides an effective means for amplifying the volume of the cathodeemissions and thus increasing the energy output of the tube. If desired,a still further increase in the electronic emissions may be obtained byusing a plurality of equipotential cathode surfaces of successivelyincreasing electron-emitting capacity, each of which is made positivewith respect to the preceding one of the series and rendered active bybombardment therefrom. A convenient arrangement for accomplishing thisresult is shown in Fig. 2, in which the electrode elements are in theform of concentrically arranged cylinders having their external surfacescoated with active material. Each of the equipotential cathodes 13, 13*,13 and 13 receives a bombardment from the 'cathode surface which itincloses, batteries 16, 16, 16 and 16 bei provided to keep eachsucceeding cath d e positive withrespect to the preceding cathode.

Where currents of relatively low periodicities are to be amplified themodification illustrated in Fig. 3 may be used. In this case anadditional input electrode 17 is employed in parallel with electrode 12and closely associated with the filament 14. T1118 arrangement operatesto increase the varia-' tion of the space current caused by the inputelectromotive force impressed through transformer 18, an increase in thevolume of the thermionic stream being occasioned by the employment of anintermediate bombarded cathode 13. The operation is some what asfollows: If we consider the input electromotive force to be such as tomake the electrode 17 momentarily positive, it is well known that therewill result an increase in the space current flowing to the cathode 18,which, in this case, serves as an anode with respect to the -filament1-1. The thermionic stream emanating from filament 11 bombards cathode13 and causes it to deliver to anode 11 an electronic stream ofincreased volume. The arrangement described is thus seen to beproductive of current variations of large amplitude in the outputtransformer 22. An inductive resistance 20 is employed in series withcathode 13 to prevent the leak of the alternating current impulses fromcathode 18 to the output circuit, which circuit includes battery 21 andthe output transformer The additional electrode 17 may conveniently bein the form of a wire, as shown in Fig. 1, and may be supported in closeproximity to the filament 14 by quartz or glass beads 19 into which boththe filament 14 and Wire 17 are fused, care being taken, of course, tokeep the two out of electrical contact with each other.

IV hat is claimed is:

1. A thermionic amplifier having two cathode surfaces, one of which isrendered electronically active from bombardment by an electronic streamemanating from the other.

2. A thermionic amplifier having two cathode surfaces, one of which isrender d electronically acti e from bombardment by a thermionic streamemanating from the other.

3. In a thermionic amplifier, a. series of cathodes of successivelyincreasing electronemitting capacity, each of said cathodes beingrendered electronically-active by bombardment from the next precedingcathode of the series;

.4. In a thermionic amplifier, a. series of cathodes of successivelyincreasing electron emitting capacity, each of said cathodes beingrendered electronically active by bombardment from the next precedingcathodeof the series, and an input circuit including an input electrodeand one of said cathodes for varying the electronic emissions from saidcathode.

5. In a thermionic amplifier, a series of cathodes of successivelyincreasing electronemitting capacity, all but one of said cathodes beingrendered electronically active by bombardment, and an input circuitincluding a plurality of input electrodes and a like number of saidcathodes for varying the electronic emissions from said cathodes.

6. In a thermionic amplifier, a plurality of cathodes of successivelyincreasing electron-emitting capacities, and means for maintaining eachof said cathodes positive with respect to the preceding cathode of theseries.

7. In a thermionic amplifier, a series of cathode surfaces ofsuccessively increasing electron-emitting capacities, means formaintaining a flow of space currentbetween each cathode and the nextsucceeding cathode, and an input electrode adjacent one of said cathodesfor varying said space current.

In witness whereof, I hereunto subscribe my name this 18th day of May A.D., 1915.

ALEXANDER MCLEAN NIGOLSON.

